Reduction of fumonisin B1 in corn grits by single-screw extrusion

This study was designed to determine the efficacy of extrusion in reducing fumonisin B1 in corn flaking grits in the presence and absence of glucose. In addition, degradation products of fumonisin B1 during extrusion were identified and quantitated with a mass balance approach. Uncontaminated clean corn grits, grits spiked with 30 microg/g fumonisin B1, and grits fermented with Fusarium verticillioides M-2552 (40-50 microg/g fumonisin B1) were extruded in the presence and absence of glucose (10%, w/w) using a single-screw extruder. Extrusion decreased fumonisin B1 by 21-37%, whereas the same process with added glucose further decreased fumonisin B1 by 77-87%. LC-fluorescence and LC-MS showed that most fumonisin in the extruded samples without added glucose was the fumonisin B1 form, whereas the main degradation product in grits extruded with glucose was N-(deoxy- d-fructos-1-yl)fumonisin B1. The formation of hydrolyzed fumonisin B1 was not significant during extrusion. Results suggest that extrusion in the presence of glucose may reduce fumonisin B1 in corn grits significantly.     

Effect of Extruding Wheat Flour at Lower Temperatures on Physical Attributes of Extrudates and on Thiamin Loss When Using Carbon Dioxide Gas as a Puffing Agent

Wheat flour with 0.3% (w/w) thiamin was extruded on a twin‐screw laboratory‐scale extruder (19‐mm barrel) at lower temperatures and expanded using carbon dioxide (CO₂) gas at 150 psi. Extrusion conditions were die temperature of 80°C and screw speed range of 300–400 rpm. Control samples were extruded at a die temperature of 150°C and screw speed range of 200–300 rpm. Dough moisture content was 22% in control samples and 22 and 25% in CO₂ samples. Expansion ratio, bulk density, WAI, and %WSI were compared between control and treatment. CO₂ injection did not significantly increase expansion ratio. Bulk densities in the CO₂ extruded samples decreased when feed moisture decreased from 25 to 22%. The products using CO₂ had lower WAI values than products puffed without CO₂ at higher temperatures. The mean residence time was longer in CO₂ screw configurations than in conventional screw configurations. Thiamin losses were 10–16% in the control samples. With CO₂, thiamin losses were 3–11% at 22% feed moisture, compared with losses of 24–34% at 25% moisture. Unlike typical high‐temperature extrusion, thiamin loss in the low‐temperature samples decreased with increasing screw speed. Results indicate that thiamin loss at lower extrusion temperatures with CO₂ injection is highly dependent on moisture content.     

Confirmation of reduced toxicity of deoxynivalenol in extrusion-processed corn grits by the MTT bioassay

The objective of this study was to determine the loss of toxicity of deoxynivalenol in extruded cereal-based products by the tetrazolium salt (MTT) bioassay using a sensitive Chinese hamster ovary (CHO-K1) cell line and to compare the results to chemical (high-performance liquid chromatography, HPLC) and biochemical (enzyme-linked immunosorbant assay, ELISA) methods of analysis. A split-split plot design was used for the extrusion process experiments at temperatures of 150, 175, and 200 degrees C and screw speeds of 70 and 140 rpm. The initial mean deoxynivalenol concentration in the corn grits artificially contaminated with Fusarium graminearum was found to be 23.5 mug/g as measured by HPLC. The percent reductions of deoxynivalenol in the contaminated corn grits upon extrusion processing ranged from 22 to 35%, from 21 to 34%, and from 21 to 37% as measured by HPLC, ELISA, and MTT bioassay, respectively. The MTT bioassay results were more closely correlated with HPLC (r = 0.90) results than with ELISA results (r = 0.78). The MTT bioassay, using a sensitive mammalian cell line, was demonstrated to be a useful method for quantification of deoxynivalenol as well as a potential toxicity screening method for contaminated extruded cereal-based products.     

Physical and biochemical properties of maize hardness and extrudates of selected hybrids

Protein and starch determinants of maize kernel hardness and extruded products were characterized to better define the role of endosperm texture during extrusion. Maize physical properties were correlated with total proteins and zein subclasses (p < 0.01). The extrusion process significantly altered protein solubility and increased protein fragmentation as measured by RP-HPLC and size exclusion chromatography. Harder grits and extrudates demonstrated higher amylose content, lower degree of starch damage, and fragmentation at different screw speeds than softer grits and extrudates. Differences in extrudate expansion ratio, water absorption index, water solubility index, oil absorption capacity, and breaking stress between harder and softer hybrids were related to protein aggregation and fragmentation as well as starch damage and fragmentation.     

Changes in Disulfide and Sulfhydryl Contents and Electrophoretic Patterns of Extruded Wheat Flour Proteins

Twin‐screw extrusion of wheat flour and the effects on the flour proteins were studied using flour samples containing 9, 20, and 30% protein. Vital gluten containing 70% protein was used to achieve the flour protein levels. The three flour samples were extruded with a twin‐screw extruder at a combination of processing parameters (exit die temperatures of 120, 140, and 160°C, and screw speeds of 240, 320, and 400 rpm). Increasing extruder exit die temperatures resulted in increased sulfhydryl content of the 9 and 20% protein content flour samples, but appeared to have little or no effect on the 30% protein content flour sample. Similarly, disulfide content decreased, albeit disproportionately, following the same trend. Both sulfhydryl and disulfide contents of extruded samples were lower than those of the nonextruded samples and could imply denaturation of protein, aggregation through intermolecular disulfide bonds, or oxidation during extrusion processing. Total cysteine content of extruded samples decreased by ≈16% relative to nonextruded samples, but otherwise remained almost unchanged among all extruded samples. The loss of total cysteine in extruded samples could represent the generation of hydrogen sulfide, volatile organic compounds, or flavor compounds during extrusion. SDS‐PAGE analysis of total proteins showed a shift from the higher to lower molecular weight regions for certain protein bands. Both depolymerization and protein aggregation occurred at higher shear forces during extrusion.     

Determination of N-(carboxymethyl)fumonisin B(1) in corn products by liquid chromatography/electrospray ionization--mass spectrometry

It is well-known that fumonisin B(1) (FB(1)) in corn meal decreases during baking, frying, and cooking, but it is still not exactly clear how heating affects the formation of N-(carboxymethyl)fumonisin B(1) (NCM-FB(1)), the reaction product of FB(1) and reducing sugars. In model experiments corn grits were spiked with FB(1) (2 mg/kg) and D-glucose (50 g/kg) or sucrose (50 g/kg) and manufactured into extrusion products at various temperatures (160--180 degrees C) and moisture levels (16--20%). A liquid chromatography/electrospray ionization-mass spectrometry method using isotopically labeled fumonisin FB(1)-d(6) as an internal standard was developed for the determination of NCM-FB(1). For sample cleanup solid-phase C18 cartridges were used. The detection limit achieved with this method was 10 ng/g (signal-noise ratio = 3:1) using the protonated molecule [M + H](+) signal of NCM-FB(1) (m/z 780) in the selected ion monitoring mode. Low concentrations of NCM-FB(1) (29-97 ng/g) were detected in all samples spiked with D-glucose and FB(1), whereas those spiked with FB(1) and sucrose showed only NCM-FB(1) in samples produced at 180 degrees C (NCM-FB(1) = 27 ng/g). Various corn-containing food samples from the German market were analyzed for the presence of NCM-FB(1), FB(1), and hydrolyzed fumonisin B(1) (HFB(1)). All samples were contaminated with FB(1) (22--194 ng/g) and HFB(1) (5--247 ng/g). Six of nine samples contained NCM-FB(1) in low concentrations ranging from 10 to 76 ng/g. From these data and the low toxicity of NCM-FB(1) it can be concluded that the significance of NCM-FB(1) in food seems to be a minor one.     

Evaluation of reduced toxicity of zearalenone by extrusion processing as measured by the MTT cell proliferation assay

The objective of this study was to determine loss of toxicity of zearalenone in extruded cereal-based products by the MTT (tetrazolium salt) cell proliferation assay using a sensitive MCF-7 human breast cancer cell line and to compare the results to chemical (high-performance liquid chromatography, HPLC) and biochemical (enzyme-linked immunosorbent assay, ELISA) methods of analysis. A split-split plot design was used for the extrusion process experiments at temperatures of 150, 175, and 200 degrees C and screw speeds of 70 and 140 rpm. The initial zearalenone concentration in the artificially contaminated corn grits with Fusarium graminearum was found at a mean concentration of 37.88 microg/g as measured by HPLC. The percent reductions of zearalenone in the contaminated corn grits upon extrusion processing were in the ranges of 67-81, 60-72, and 66-78% as measured by HPLC, ELISA, and the MTT cell proliferation assay, respectively. The MTT cell proliferation assay results were more closely correlated with HPLC results (r = 0.96) than ELISA results (r = 0.83). The MTT cell proliferation assay was demonstrated to be a useful method for quantification of zearalenone as well as a potential toxicity screening method for contaminated extruded cereal-based products.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches II. Morphological and Molecular Characterization

A series of cross‐linked hydroxypropylated corn starches were extruded with a Leistritz micro‐18 co‐rotating extruder. Extrusion process variables including moisture (30, 35, and 40%), barrel temperature (60, 80, and 100°C), and screw design (low, medium, and high shear) were investigated. Scanning electron microscopy (SEM) of extruded starches showed a gel phase with distorted granules and granule fragments after extrusion at 60°C. After extrusion at 100°C only a gel phase was observed with no granular structures remaining. High performance size exclusion chromatography (HPSEC) equipped with multiangle laser light‐scattering (MALLS) and refractive index (RI) detectors showed extruded starches degraded to different extents, depending on extrusion conditions. The average molecular weight of the amylopectin of unextruded native corn starch was 7.7 × 10⁸. Extrusion at 30% moisture, 100°C, and high shear reduced the molecular weight of amylopectin to 1.0 × 10⁸. Hydroxypropylated normal corn starch extruded at identical conditions showed greater decreases in amylopectin molecular weight. With the addition of cross‐linking, the amylopectin fractions of the extruded starches were less degraded than those of their native and hydroxypropylated corn starch counterparts. Similarly, increasing moisture content during extrusion lowered amylopectin degradation in the extruded starches. Increasing temperature during extrusion of cross‐linked hydroxypropylated starches at high moisture content (e.g., 40%) lowered amylopectin molecular weights of the extruded starches, whereas increasing extrusion temperature at low moisture content (30%) resulted in less degraded molecules. This difference was attributed to the higher glass transition temperatures of the cross‐linked starches.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches I. Pasting Properties

A series of cross‐linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro‐18 co‐rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X‐ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross‐linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross‐linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).     

Effects of Extruder Screw Speeds on Physical Properties and In Vitro Starch Hydrolysis of Precooked Pinto,Navy, Red,and Black Bean Extrudates

Precooked pinto, navy, red, and black bean flours were extruded at different screw speeds (320, 380, and 440 rpm) with a twin‐screw extruder. Effect of speed on physical properties and in vitro starch hydrolysis was investigated. Increasing screw speeds reduced water activity, expansion index, and texture. Extrudates could not be obtained from pinto bean flour at 440 rpm because of the high shear effect. Water absorption index and water solubility index were not significantly affected by screw speed but were significantly higher than for unextruded precooked flour. A significant change in color was observed in navy beans, characterized by increasing b values on the Hunter color scale. Resistant starch ranged from 3.65 to 4.83% db and was not significantly affected by screw speed. Glycemic index of all extrudates was high, ranging from 81.3 to 86.9.     

Oil Absorption Characteristics of a Multigrain Extrudate During Frying: Effect of Extrusion Temperature and Screw Speed

The oil absorption characteristics of a multigrain extruded and fried snack product were studied as a function of extruder screw speed and cooking temperature using a central composite response surface methodology (RSM). The extruded product was produced using a corotating twin screw extruder, dehydrated to a uniform moisture content, and subsequently deep‐fat‐fried at 192 ± 1°C for 10–40 sec to complete expansion. Significant RSM models were developed for oil absorption and extrudate water absorption index (WAI). According to the lowest oil model, absorption (19.9%) was obtained with an extruder screw speed of 218.6 rpm and a cooking temperature of 117.8°C. WAI reached a maximum at a screw speed of 221.9 rpm and a cooking temperature of 109°C. Oil absorption characteristics and extrudate WAI were significantly correlated (r= ‐0.84, P = 0.0002). The data suggest that extrusion conditions can be optimized to influence the physicochemical structures in the extrudate matrix so that oil absorption can be minimized.     

Extrusion and Characterization of Starch Films

Starch plasticized with water, glycerol, and stearic acid was extruded and sheeted into films 0.4–0.6 mm thick. The ingredients were extruded in a conical twin‐screw extruder at a temperature profile of 50–120–120–120°C and a screw speed of 45 rpm. The effects of glycerol, water, and stearic acid on selected physical and functional properties of the films were studied. The tensile strength, tensile strain at break, and Young's modulus were 0.23–2.91 MPa, 45.79–90.83%, and 2.89–37.94 MPa, respectively. Differential scanning calorimetry thermograms exhibited two glass transitions and multiple melting endotherms, including that of amylose‐lipid complexes formed during extrusion. The enthalpy of gelatinization of starch in the extruded films was 0.7–4.1 J/g and was dependent largely on the plasticizer content. Fourier‐transform infrared spectra revealed significant interactions between the starch and plasticizer but the peaks shifted to higher wave numbers with increasing glycerol content. During extrusion in the presence of glycerol, the A‐type crystalline structure of starch was transformed to B‐type. It also was observed that the V_h crystallinity increased with increase in glycerol content due to tight packing of starch chains. The water vapor permeabilities of the starch films were 12.3–19.9 g·mm/hr·m²·kPa.     

Using an In‐Line Slit‐Die Viscometer to Study the Effects of Extrusion Parameters on Corn Melt Rheology

An in‐line slit‐die viscometer (SDV) was used to measure the viscosity of a melt extrudate independently of the extruder operating conditions. The melt produced by extrusion of the corn grits followed a power law rheological model. The viscosity of the melt and extrusion parameters such as specific mechanical energy (SME), torque, and die pressure decreased with increasing moisture content. The degree of starch gelatinization increased when barrel temperature increased from 90 to 130°C. At temperatures higher than 130°C, most of the starch had gelatinized. The increase in barrel temperature, however, resulted in small changes in the apparent viscosity of the melt, until a maximum of ≈130°C. At a constant feed rate, SME increased and torque decreased when screw speed increased due to the shear thinning behavior of the melt. At a constant screw speed, the torque increased and SME decreased with increasing feed rate. This was due to a decrease in apparent viscosity of the melt at higher feed rates. SME is not an independent extrusion variable and should be used with caution either when predicting the effect of thermomechanical treatment of the product or as the key and only variable for controlling the food extrusion process.     

Effect of Amylose Content on Expansion of Extruded Rice Pellet

Rice pellets were prepared by single‐screw extrusion cooking with an in‐barrel water content of 50 wt%. Three different types of rice, indica glutinous, japonica, and indica, were used as raw materials. Reconstituted rice flour was made to study the effect of amylose content on pellet expansion. The glass transition (T_g) and expansion (T_e) temperatures of extruded pellet were determined by differential scanning calorimetry (DSC) and noncontact infrared thermometer, respectively. The amylose content was not significantly affected by extrusion cooking. The reduction in intrinsic viscosity indicated that amylopectin experienced some degradation. The T_g and T_e were not functions of amylose content, which affected the expansion ratio of the pellets. The Gordon‐Taylor equation was applied to estimate the T_g of the rice pellets.     

Effect of Barley Flour on Development of Rice‐Based Extruded Snacks

This study was conducted to develop a ready‐to‐eat extruded food using a single‐screw laboratory extruder. Blends of Indian barley and rice were used as the ingredients for extrusion. The effect of extrusion variables and barley‐to‐rice ratio on properties like expansion ratio, bulk density, water absorption index, hardness, β‐glucan, L*, a*, b* values, and pasting characteristics of extruded products were studied. A central composite rotatable design was used to evaluate the effects of operating variables: die temperature (150–200°C), initial feed moisture content (20–40%), screw speed (90–110 rpm), and barley flour (10–30%) on properties like expansion ratio, bulk density, water absorption index (WAI), hardness, β‐glucan, L*, a*, b* values, and sensory and pasting characteristics of extruded products. Die temperature >175°C and feed moisture <30% resulted in a steep increase in expansion ratio and a decrease in bulk density. Barley flour content of 10% and feed moisture content of <20% resulted in an increased hardness value. When barley flour content was 30–40% and feed moisture content was <20%, a steep increase in the WAI was noticed. Viscosity values of extruded products were far less than those of corresponding unprocessed counterparts as evaluated. Rapid visco analysis indicated that the extruded blend starches were partially pregelatinized as a result of the extrusion process. Sensory scores indicated that barley flour content at 20%, feed moisture content at 30%, and die temperature at 175°C resulted in an acceptable product. The prepared product was roasted in oil using a particular spice mix and its sensory and nutritional properties were studied.     

Extrusion of Regular and Waxy Barley Flours for Production of Expanded Cereals

Grains of two regular and two waxy barley cultivars were milled into break and reduction stream flours using a wheat milling mill, granulated to facilitate feeding and flow through the barrel, and extruded to form expanded products using a modified laboratory single‐screw extruder. As moisture content of barley granules decreased from 21 to 17%, the expansion index of extrudates increased from 1.81 to 2.68, while apparent modulus of compression work (AMCW) decreased from 17.1 × 10⁴ to 7.8 × 10⁴ N/m². Break stream flours of both regular and waxy barley produced extrudates with higher expansion index (2.72–3.02), higher water absorption index (WAI), and lower AMCW than extrudates from reduction stream flours. Extrudates produced from regular barley had generally higher expansion and lower density than those produced from waxy barley. The specific mechanical energy (SME) was greater during extrusion of regular than of waxy barley. Barrel temperatures of 130, 150, and 170°C for the feeding, compression, and metering sections, respectively, resulted in higher SME, higher expansion index, lower water absorption index and lower AMCW of extrudates compared with a constant extruder barrel temperature of 160°C. Increased screw speed generally resulted in larger expansion index and increased WAI of extrudates. With increased feed rate from 89 to 96 g/min, the expansion index of extrudates decreased from 3.20 to 2.78 in regular barley and 3.23 to 2.72 in waxy barley, and harder extrudates were produced.     

Physical Characteristics,Nutritional Quality,and Antioxidant Potential of Extrudates Produced with Polished Rice and Whole Red Bean Flours

In Brazil, rice (Oryza sativa L.) and beans (Phaseolus vulgaris L.) are the basis of the population's diet, and their consumption together is a good strategy to improve protein biological value. The aim of this study was to produce extruded products with whole red bean (WRBF) and polished rice (PRF) flours and to evaluate the effects of extrusion temperature (T) and feed moisture content (FM) on technological properties and total phenolic compounds content. The extrudates were elaborated in a twin‐screw extruder following a 2² central composite rotatable design with FM (15–23%) and T (120–160°C) as independent variables. WRBF and PRF were used at a 1:3 ratio. Amino acid content and profile were evaluated in the optimum extrudate (produced at FM = 19% and T = 140°C). The total phenolic content identified in extruded products was provided by the red bean seed coat, and its quantification suggested the release of bound phenolics with the extrusion process (not temperature dependent). The extrusion of PRF and WRBF, in combination, produced extruded products of high protein quality, being complete in essential amino acids for the diets of people at least 48 months old. The results indicate that legume flours such as WRBF incorporated into rice flour can cause a positive impact on technological, nutritional, and functional quality of extrudates.     

Enzyme-assisted extraction of moniliformin from extruded corn grits

Water has been known to be the ideal solvent for moniliformin but is not suitable to extract this toxin from cooked matrices due to instant swelling upon addition of the solvent. In this study, an improved method to extract moniliformin from extruded corn grits using alpha-amylase was developed. In an effort to optimize the method, the efficacy of using a protease was also studied. Treatment with alpha-amylase resulted in a clear solution with decreased suspended solid content as measured by transmittance (%T), which improved from 0 to 96% in 10 min. The detected level of moniliformin from extruded corn grits was increased to 4.02 mug/g when extracted with 1% tetrabutylammonium hydrogen sulfate following alpha-amylase treatment compared to 2.56 microg/g when it was extracted with 90% acetonitrile without enzyme treatment. The average recovery of moniliformin from extruded corn grits was 96% when alpha-amylase was used in the extraction procedure. Overall, the amounts of moniliformin detected in extruded corn grits increased significantly by using enzyme hydrolysis. Chromatographic separation was also benefited by lesser interference and improved peaks.     

Effects of Calcium Hydroxide and Processing Conditions on Corn Meal Extrudates

The effects of added calcium hydroxide (0.0, 0.15, 0.25, and 0.35%) and processing conditions, feed moisture content (mc) (16, 18, and 20%) and barrel temperature (130 and 150°C) on characteristics of corn meal extrudates were studied. Extruder screw speed was maintained at 130 rpm. Corn meal was extruded with a single-screw extruder (Brabender model GNF 1014/2) with a screw compression ratio of 3:1. The highest values (P < 0.05) for radial expansion and the lowest values for density and breaking force of extrudates were found for the treatment with 0.00% calcium hydroxide extruded at 16% feed mc and 130°C barrel temperature. This treatment was statistically different from the other treatments. Best values for radial expansion of samples extruded with added calcium hydroxide were for the samples with 0.15% calcium hydroxide at 18% feed mc and 130°C barrel temperature, followed by the sample with 0.35% calcium hydroxide at 16% feed mc and 130°C barrel temperature. Water absorption index and water solubility index were affected by calcium hydroxide and extrusion conditions evaluated. Extrudates had large numbers of flattened and sheared granules. Increases in calcium hydroxide increased extrudate yellowness. The combined action of calcium hydroxide and extrusion conditions completely modified the organized structure of the starch and suggest the formation of a starch-calcium complex (crystalline region). The texture of the extruded products was crispy after puffing.     

Effect of Sucrose on Starch Conversion and Glass Transition of Nonexpanded Maize and Wheat Extrudates

Nonexpanded “half products” were prepared by twin‐screw extrusion of maize and wheat of fine and coarse particle size in three levels of sucrose, 0, 10, and 20% db. The degree of starch conversion in the extrudates was determined using X‐ray diffraction, differential scanning calorimetry, and rapid viscosity analysis. Starch conversion was greater in the fine material compared with the coarse material and greater for wheat compared with maize. Sugar addition decreased starch conversion in all cases, but the effect was greater for maize compared with wheat and for the coarse material compared with the fine material. The thermal mechanical properties were studied by dynamic mechanical thermal analysis to determine the effect of sugar on the glass transition temperature (T_g) in the four different materials. As expected, the mechanically determined T_g was reduced by sugar addition. Water plasticized wheat semolina less than the other three materials. It was suggested that this was because the extruded semolina was entirely amorphous, whereas Xray analysis showed some crystallinity in the other three materials. Die swell was much less for maize grits possibly because elasticity decreased with decreasing starch conversion. The implications for the role of both water and sugar on the behavior of directly expanded extrudates are discussed.